The present invention is intended to address two concerns. The first problem involves the accumulation of used tires in landfills, dumps, and recycling facilities, due to the lack of an adequate market for recycled rubber. Used tires can be burned or pyrolyzed as a means of disposal; however, this alternative is hazardous due to the hazardous gases that can be produced by pyrolysis or burning as well as the basic pollution problems that are incurred with combustion processes in general. Burning of GTR can produce significant pollutants including dioxins.
The second problem arises from the need of cheap soft thermoplastic elastomers that have potential to be recycled by recovery technology as opposed to thermoset rubber.
A thermoplastic elastomer is generally defined as a polymer or blend of polymers that can be processed and recycled in the same way as a conventional thermoplastic material, yet has properties and performance similar to that of vulcanized rubber at service temperatures. For example, U.S. Pat. No. 5,157,082 (Johnson) discloses compositions comprising ground vulcanized rubber, polyolefin and a functionalized olefin polymer. Compositions of this type, however, those compositions tend to have relatively low ultimate elongation and tear strength.
Specifically, U.S. Pat. No. 5,733,943 to Doan discloses a process and composition for the manufacture of a street sign material using reground rubber from used tires in a blend with a styrene-butadiene copolymer and polypropylene or polyethylene mixed in a heated extruder to produce the final product.
In U.S. Pat. No. 6,015,861 to Mertzel et al., a composition comprising finely ground cross-linked rubber with a compatibilizer and thermoplastic material is prepared by a simple mixing technique using an extruder or other form of mixer. Both Doan and Mertzel et al. differ from the present invention in that neither of them uses ground rubber component for devulcanization. In US 20020113333 to Liu et al., a composition provides phase compatibility treatment with reactive blending of the rubber with a free radical generating compound as peroxide and azo.
In US 20070264495 to Resmini, a composition comprising coupling agent having at least one ethylenic unsaturation is used. Coupling agent improves the compatibility between the styrene-based thermoplastic elastomers and the ground vulcanized rubber particles and allows obtaining a thermoplastic elastomer having good mechanical properties, in particular stress at break and elongation at break. Moreover, the Melt Flow Index (MFI) of said thermoplastic elastomer is not negatively affected.